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    <script>
        var a = [1, 2, [3, [4, 5, [1, 2, 3]], 4, 5], 6, [7, 8], 9];

//从头开始遍历，检验每个元素的长度，如果长度为1 直接打印，
//长度不为1，递归循环
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                if (!isNaN(arr[i])) {
                    console.log(arr[i]);
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